Seaming of Composite Tapes

IntroductionKVE Composites Group is a company specialized in composites. They mainly serve the aerospace, defence and machine construction industries. Services they deliver include product design, engineering and manufacturing, but also repairing or R&D.

Problem

For most of their products composite ‘tape’ is used. This is a very thin sheet of fibres with matrix. The tapes are placed on top of each other, each with a different direction. Then the tapes are consolidated to make a stiff composite plate that is strong in multiple directions. At this moment the tapes are delivered in narrow rolls, but for most products a wider sheet of this tape is required. That is why two tapes are seamed together, so that it makes one wider sheet. This process can be repeated as often as they like to create really wide sheets, or even rolls with the fibers at a 90 or 45 degree direction.

Composite tape on roll

The seaming of the tapes is now done by hand. This is a tough job that takes a lot of time and the quality isn’t very good. Bad quality can lead to multiple problems in the construction where the tape is used, including ugly spots, destruction of the seam during construction, or overlap of the sheets, thus causing a bulge in the plate.

Assignment

The system needs to check if the tapes are aligned in the correct way, after that it needs to seam the two tapes together and check if the seam is seamed correctly. The tapes can differ in size and material, so the system needs to be easily adjustable to accommodate the different sizes and materials. Ideally there is some sort of data feedback, so the company can iterate on the process themselves.

The following suggestions are out of our scope, but we took it in mind while designing the current system:

The full system can be made including a supply system for supplying the tape into the seaming system (the cutting of the tapes is currently done by hand)

The full system will have a storage system for rolling up the seamed tapes on a roll (the seamed tapes are currently not coiled).

The system seams tapes in different orientations: 0 degrees, 45 degrees and 90 degrees.

Solution

The full job (cutting – seaming – storing) in the way it is currently done is too ambitious and time consuming to implement fully in this project.

The designed concept system automates the most precise and time-consuming part: the seaming. The cutting and storing of the parts will still be done manually.

A 3D-CAD of the designed concept system can be found below. The full system is 3.5 meters wide and 1 meter long, to enable the system to seam tapes of 2.35 meters. In the middle of the table there is a glass plate with lighting underneath, this is used for the alignment and quality checks. The light makes it easier to see gaps in the alignment. It has a clamping system that makes sure the tapes won’t move after the initial alignment. The main movement of the system is done through means of a linear rail. The cart of this linear rail has a mount for the soldering iron and a camera.

Concept design

The tapes will be placed in a way that the seam will be made on the glass. This is made easier by the alignment-system with slides which can be set to tape width only once to accommodate for good alignment every time. Before clamping and checking, some values are needed. The type of material needs to be entered, the used temperature of the soldering iron and the speed of the linear rail. When the tape is clamped, the camera will do an alignment check (the linear rail cart moved over the clamped tapes) and the alignment will be approved or rejected by the vision software. There is also an option where the vision program is not sure about the alignment, and will ask for a visual check. If the alignment is approved, the soldering iron will be lowered to seam the two tapes together. The linear cart moves very slowly over the tapes while the soldering iron is melting the matrix of the composite tapes together.

The camera is mounted behind the soldering iron. This means the quality check can be done at the same time as the tapes are being seamed. The pictures, information about the quality of the seam and the temperature will be processed and saved by giving the picture a unique name which includes the speed, material and temperature. Also a graph is added which pronounces the gap that is left after the seaming, so the quality of the seam can be properly seen. This way all the data of the seam is stored for every seam and available for quality review. When this process is finished the clamping is released and the tapes are seamed together.

Proof of conceptThe designed concept system would take too much time to make in the available time. For this minor it was decided that a proof of concept system would be made. The set-up is smaller and was done with components available in the robotics lab.

Proof of concept setup

This proof-of-concept system works in the same way as the designed concept system and the software is designed in such a way that it can be upscaled very fast. In this proof of concept only tapes with a Nylon matrix were regularly seamed, due to lower melting temperature and lower price. But theoretically the machine will also work for the more high-end tapes. The HMI consist of three fields to enter the required values and a start and stop button to run the python script. In the Settings tab the vision script and the output folder for the pictures can be selected. The debugging tab shows the exact command that LabVIEW sends to the command prompt as well as the output of the command prompt and possible errors.

HMI for proof of concept

In the proof of concept, all the data is stored with the pictures, but since the hardware was somewhat different from the intended specs of the prototype, we have eventually used manual speed and temperature control. Further integration is necessary to ensure the process becomes fully integrated. However the seaming worked with a moderate degree of success, and the quality control and data feedback worked with a good degree of success. One of the seaming result pictures with the data stored in the name of the picture can be seen in the pictures below.

Unique name including seaming parameter data

Post seam picture including remaining gap size graph

With the output data, KVE can find out what parameters give the best quality seams, and optimize this process.